The present invention relates generally to rotatable members that are able to achieve balanced conditions throughout a range of rotational speeds. The present invention also relates to methods and symptoms for dynamically balancing rotatable members through the continual determination of out-of-balance forces and motion to thereby take corresponding counter balancing action. The present invention additionally relates to methods and systems in which inertial masses are actively placed within a rotating body in order to cancel rotational imbalances associated with the rotating body thereon. The present invention additionally relates to methods and system that establish consistent measurement thresholds applied to assessing the immediate balance condition for determining the course of dynamic balance control.
Mass unbalance in rotating machinery leads to machine vibrations that are synchronous with the rotational speed. These vibrations can lead to excessive wear and to unacceptable levels of noise. Typical imbalances in large, rotating machines are on the order of one inch-pound.
It is a common practice to balance a rotatable body by adjusting a distribution of moveable, inertial masses attached to the body. Once certain types of bodies have been balanced in this fashion, they will generally remain in balance only for a limited range of rotational velocities. A tire, for instance, can be balanced once by applying weights to it. This balanced condition will remain until the tire hits a very large bump or the weights are removed. A centrifuge for fluid extraction, however, can change the amount of balance as more fluid is extracted.
Many machines are also configured as freestanding spring mass systems in which different components thereof pass through resonance ranges until the machine is out of balance. Additionally, such machines may include a rotating body flexibly located at the end of a shaft rather than fixed to the shaft as in the case of a tire. Thus moments about a bearing shaft may also be created merely by the weight of the shaft. A flexible shaft rotating at speeds above half of its first critical speed can generally assume significant deformations, which add to the imbalance. This often poses problems in the operation of large turbines and turbo generators.
Machines of this kind usually operate above their first critical speed. As a consequence, machines that are initially balanced at relatively low speeds may tend to vibrate excessively as they approach full operating speed. Additionally, if one balances to an acceptable level rather than to a perfect condition (which is difficult to measure), the small remaining out of balance will progressively apply force as the speed increases. This increase in force is due to the fact that Fxcex1rxcfx892, (i.e., note that F is the out-of-balance force, r is the radius of the rotating body and (xcfx89 is its rotational speed).
The mass unbalance distributed along the length of a rotating body gives rise to a rotating force vector at each of the bearings that support the body. In general, the force vectors at respective bearings are not in phase. At each bearing, the rotating force vector may be opposed by a rotating reaction force, which can be transmitted to the bearing supports as noise and vibration.
The purpose of active, dynamic balancing is to shift an inertial mass to the appropriate radial eccentricity and angular position for canceling the net mass unbalance. At the appropriate radial and angular distribution, the inertial mass can generate a rotating centrifugal force vector equal in magnitude and phase to the reaction force referred to above.
Many different types of balancing schemes are known to those skilled in the art. When rotatable objects are not in perfect balance, nonsymmetrical mass distribution creates out-of-balance forces because of the centrifugal forces that result from rotation of the object. Although rotatable objects find use in many different applications, one particular application is a rotating drum of a washing machine.
U.S. Pat. No. 5,561,993, which issued to Elgersma et al. on Oct. 22, 1996, and is incorporated herein by reference, discloses a self-balancing rotatable apparatus. Elgersma et al. disclosed a method and system for measuring forces and motion via accelerations at various locations in a system. The forces and moments were balanced through the use of a matrix manipulation technique for determining appropriate counterbalance forces located at two axial positions of the rotatable member. The method and system described in Elgersma et al. accounted for possible accelerations of a machine, such as a washing machine, which could not otherwise be accomplished if the motion of the machine were not measured. Such a method and system was operable in association with machines that are not rigidly attached to immovable objects, such as concrete floors. The algorithm disclosed by Elgersma et al. permitted counterbalance forces to be calculated even though a washing machine is located on a moveable floor structure combined with carpet padding and carpets between the washing machine and a rigid support structure.
U.S. Pat. No. 5,561,993 thus described a dynamic balance control algorithm for balancing a centrifuge for fluid extraction. To accomplish such balance control, sensor measurements may be used to assess the immediate balance conditions and determine the course of balance control. Related sensor responses to balance control actions may be modeled to determine the specific future control actions. In assessing the balance condition, measurement thresholds can be established (e.g., balance-threshold, maximum-threshold). In the case where acceleration measurements are utilized directly, thresholds change with rotational speed and the relation to the perceived balance is not intuitive. Thus, it is difficult to establish consistent criteria across multiple sensors, sensing axes, and full operating ranges. This often results in transitions to stricter threshold criteria at higher rotational speeds, which cannot be met. Also, when utilizing force and acceleration measurements, it is often difficult to determine their relative importance in describing the balance condition. This often results in inadequate balancing at some speeds while over balancing at others.
The present inventor has thus concluded, based on the foregoing, that a need exists for a method and system for measuring the dynamics of a rotating system and relating those sensor measurements to the balance condition in a manner that provides consistent criteria across multiple sensors, sensing axes, and rotational speeds, and which additionally is based on simple computational algorithms. The present inventor believes that the invention described herein can overcome these obstacles through the utilization of a signal-energy-based measuring scheme, which can directly relate thresholds to perceived balance conditions and provide consistency in multiple sensor measurement configurations.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
In accordance with addressing the shortcomings of the prior art, it is one aspect of the present invention to provide methods and systems in which rotatable members can achieve balanced conditions throughout a range of rotational speeds.
It is another aspect of the present invention to provide methods and systems for dynamically balancing rotatable members through the continual determination of out-of-balance forces and motion to thereby take corresponding counter balancing action.
It is yet another aspect of the present invention to provide methods and systems for measuring the dynamics of rotating systems and devices thereof in order to make corrections necessary to placing such systems or devices in a balanced condition.
It is still another aspect of the present invention to provide methods and systems for dynamic balancing of rotating system using energy-based threshold measurements to determine the course of balance control.
In accordance with various aspects of the present invention, methods and systems are disclosed herein for dynamically balancing a rotating system utilizing energy-based threshold measurements, wherein the rotating system contains sensors therein. Sensor measurements are compiled from the sensors. The sensor measurements contain data indicative of the dynamics of the rotating system. The sensor measurements are converted to signal-energy values, or values proportional to signal-energy, associated with the rotating system. The signal-energy values can then be compared to predefined signal-energy threshold values to thereby determine the proper course for balancing corrections necessary to dynamically place the rotating system in a balanced state or change rotational speed.
Additionally, a predefined signal-energy threshold profile may be converted into a sensor measurement threshold profile for direct comparison to the sensor measurements. When force and acceleration measurements are used to assess the balance condition, wherein the measurement represents the simple sinusoidal component of the sensed signal at the speed of rotation, managing the signal-energy relates proportionally to maintaining physical displacement. The signal-energy threshold profile becomes a displacement threshold profile, with an intuitive association to the balance condition, which may be converted to force and acceleration sensor measurement threshold values associated with a range of rotational speeds. Thereafter, the sensor measurements may be compared to the force and acceleration threshold values, thereby determining proper course for balancing corrections necessary to dynamically place the rotating system in a balanced state or change its rotational speed.